A Long Term Evolution (LTE) group communications system is a special communications system with a scheduling capability. In a current LTE group communications system, information may be transmitted in two manners: unicast and multicast. Referring to FIG. 1, FIG. 1 is an architectural diagram of an existing LTE group communications system. A group communication service application server (GCS AS) transmits user data to user equipment (UE) based on the Real-Time Transport Protocol (RTP). A packet header of an RTP packet transmitted by the GCS AS to the UE includes synchronization source information of the GCS AS.
In the unicast transmission manner, the GCS AS sends an RTP packet to the UE by using a public data network (PDN) gateway (P-GW), a serving gateway (S-GW), and an evolved NodeB (eNB). After receiving the RTP packet, the UE obtains synchronization source information of the GCS AS by parsing a packet header, and adds the synchronization source information of the GCS AS to a trust list.
In the multicast transmission manner, the GCS AS first sends an RTP packet to a broadcast/multicast service center (BM-SC). After receiving the RTP packet from the GCS AS, the BM-SC changes synchronization source information of the GCS AS in the RTP packet into synchronization source information of the BM-SC, and then sends a changed RTP packet to the UE by using a Multimedia Broadcast Multicast Service gateway (MBMS GW) and an eNB. After receiving the RTP packet, the UE obtains the synchronization source information of the BM-SC by parsing a packet header, and adds the synchronization source information of the BM-SC to a trust list.
In the prior art, when UE is in an inactive Multimedia Broadcast Multicast Service (MBMS) coverage area, a GCS AS can send an RTP packet to the UE only in a unicast manner. When the UE is in an MBMS coverage area and a multicast condition is met, the GCS AS can send an RTP packet to the UE in a multicast manner.
However, assuming that the UE is moved from the non-MBMS coverage area to the MBMS overage area, a transmission manner may be switched from a unicast manner to a multicast manner. In a unicast process, the UE adds only synchronization source information of the GCS AS to a trust list. Therefore, when the UE receives an RTP packet sent by a BM-SC, because synchronization source information of the BM-SC that is included in the received RTP packet is not in the trust list, the UE may consider the RTP packet from the BM-SC as an invalid RTP packet and discard the RTP packet. In contrast, when the UE is moved from the MBMS coverage area to the non-MBMS overage area, the UE adds only the synchronization source information of the BM-SC to the trust list. Therefore, when the UE receives an RTP packet sent by the GCS AS, because synchronization source information of the GCS AS that is included in the received RTP packet is not in the trust list, the UE may consider, as an invalid RTP packet, the RTP packet transmitted by the GCS AS in a unicast manner and discard the RTP packet. Therefore, in the prior art, after a transmission manner is switched between a unicast manner and a multicast manner, a technical problem that the UE discontinuously receives RTP packets may be caused.